Installation to heat the productive zone of the reservoir of a hydrocarbon extraction well

ABSTRACT

A heating installation for the productive zone of the reservoir of a well for the extraction of hydrocarbons through a well linking the surface to this reservoir, including a substantially cylindrical casing consolidating the wellbore and hydrocarbon extraction method housed inside the casing and method enabling a hot heat-transfer fluid to be injected from the surface to the reservoir. The installation includes through the well a first thermally insulated tubing of injection of the hot fluid from the surface to the reservoir, second tubing surrounding the first tubing to return the hot fluid to the surface and a third tubing to extract the hydrocarbons independent from the first and second tubing, the tubings extending from the surface to the reservoir.

The technical scope of the present invention is that of heating installations for the reservoir of a well for the extraction of hydrocarbons present in geological reservoirs.

It is known today to extract liquids from the ground, for example hydrocarbons, that lie in underground reservoirs that can be several kilometres in the ground. After drilling a hole from the surface to the reservoir containing the liquid to be extracted, this hole is consolidated as it is being drilled by pipes of decreasing diameters. This set of pipes constitutes a casing. In the productive zone, towards the buried end, this casing is perforated by a certain number of openings so as to provide access for the liquid. This perforated part is called screen or drain depending on its length. A pipe of constant diameter and less than that of the casing is introduced into the said casing so as to reach the bottom of the wellbore to pump the liquid to the surface. This pipe is thus extraction tubing. This tubing may be equipped with a well-bottom pump.

One frequently encountered problem is the low value of the absolute or total flow of the wellbore. This flow is linked to several factors, but it is essentially the viscosity of the liquid extracted that causes problems. This liquid is all the more viscous in that its temperature is low. According to the composition of the liquids to be extracted, another problem may appear. In the case of a liquid containing fractions that can solidify, for example paraffin or asphaltene, these fractions have a tendency to solidify, all the more so when the temperature is low. These fractions tend to settle and gradually block the openings of the productive zone, in the casing, and in the reservoir itself in the vicinity of the casing.

It can be observed, therefore, that the high viscosity and the solid deposits lead to a reduction in said flow rate, thereby increasing the cost of production per unit of volume, which may eventually lead to the closure of the well.

So as to overcome this problem, several solutions have been proposed. Reference may be made, for example, to patents U.S. Pat. Nos. 2,757,738 and 4,244,485.

One solution consists injecting a solvent for the heavy fractions into the reservoir zone. One drawback to this lies in the necessity of providing logistics around this solvent: supply, storage, etc. Another drawback lies in the fact that the chemical action of the solvent only operates on certain fractions.

Another solution by heating consists in positioning a heater, at the well bottom in the drain. This heater is advantageously an electrical resistance. The difficult diffusion of this thermal power generates very high temperatures. This raises the problem of the choice of materials, both for the resistance and for the extremity of the casing and/or extraction tubing. Given its location at the well bottom, it is difficult to provide a reliable and easily maintainable resistance. For safety reasons lastly, it is difficult to bring large quantities of electrical energy, typically 100 to 500 kW, to the bottom of a well.

Another solution consists in injecting, by means of the extraction tubing, pressurized water steam. There are several drawbacks to this method. Given the considerable length of a well, which can reach several kilometres, it is difficult to guarantee that the steam will still be hot when it reaches the well bottom. Moreover, using extraction tubing for this reason requires the total shutdown of production during this phase. This method suffers the drawback of causing discontinuous production (known as Huff n' Puff).

It is known that the injection of heat into an oil well facilitates the flow from the productive rock through the screen or drain. The heat acts in two ways: it reduces the viscosity of the crude oil thereby facilitating its flow and it prevents the formation of deposits, paraffin and asphaltene, or even melts them if there were deposits dating before the injection of heat.

The methods using a heat supply have a two-fold effect. They act on the deposits and on the fluidity of the heated liquid, thereby increasing the extractable flow rate and the efficiency of the extraction.

Lastly, reference may also be made to patent FR-2881788 which discloses a device in which a hot fluid is made to circulate so as to bring the rock locally to a higher potential temperature by conduction so as to fluidize the hydrocarbons, by means of thermally insulated tubing. The hot fluid is recovered mixed with the hydrocarbons. The drawback to this device lies in that the hot fluid is mixed with the hydrocarbons extracted from the productive zone and thus the flow rate that the well bottom pump has to cope with must be increased by a factor of 5 to 30 depending on the flow rate and the increase in production of the well.

In the case where the heat transfer fluid is water, the mixture thus formed must be separated at the surface.

Another drawback to this device in the case where the surface-heated fluid is the fluid extracted from the well, lies in that the boiler required to heat this fluid must be dimensioned to heat a hydrocarbon mixture containing heavy elements and also a portion of water. The boiler will be all the more difficult to dimension and will be more expensive. For example, the heating elements of the boiler must have a power flux density that is lower than required for a thermal oil. The maintenance of a boiler heating a mixture of heavy hydrocarbons requires the deposits that can appear on the heating elements to be controlled.

The aim of the present invention is to supply a system to improve the productivity of a well and increase the recoverable reserves by supplying heat to the reservoir in the productive zone of the reservoir of a well by separating the heat transfer fluid and the extracted hydrocarbons.

The invention thus relates to a heating installation for the productive zone of the reservoir of a well for the extraction of hydrocarbons through the well linking the surface to a reservoir, comprising a substantially cylindrical casing consolidating said well and a hydrocarbon extraction means housed inside said casing and means enabling a hot heat-transfer fluid to be circulated from the surface to the reservoir, wherein it comprises through the well a first thermally insulated tubing of injection of the hot fluid from the surface to the reservoir, a second tubing surrounding the first tubing to return the hot fluid to the surface and a third tubing of extraction of the hydrocarbons independent from the first and second tubing, said tubings extending from the surface to the reservoir.

The surface equipments are composed of a storage or an expansion tank, a pump and a heater. The hot fluid leaving the heater circulates in the thermally insulated tubing to its end and then returns to the surface between the thermally insulated tubing and the second heating tubing.

According to one characteristic of the invention, the first and second tubing are linked to a hot fluid production unit provided with a storage or expansion tank, a pump and a heater to ensure a continuous circulation of the hot fluid in said tubings.

According to another characteristic of the invention, the first tubing is open at its distal end and the second tubing is closed at its distal end.

According to yet another characteristic of the invention, the first tubing is thermally insulated by means of a compression-resistant insulation, either by its compressive resistivity properties or by the addition of spacers evenly positioned between the first and the second tubing.

Advantageously, the third tubing is linked to an extraction unit to bring the hydrocarbons produced in the screen or drain to the surface.

According to yet another characteristic of the invention, the third tubing is open at its distal end and is provided with a well-bottom pump.

According to yet another characteristic of the invention, the first tubing is constituted by a first inner pipe surrounded by a second concentric outer pipe and by an insulation housed in the space between the two pipes.

Advantageously, the thermal insulation is a microporous material and a reduced pressure is established in the space between the two pipes.

According to yet another characteristic of the invention, the reduced pressure between the two pipes of the first tubing is of between 1 and 100 mbar.

According to yet another characteristic of the invention, the first tubing is provided with an electrical heating wire arranged against the inner wall of the inner pipe.

According to yet another characteristic of the invention, the heat-transfer fluid to heat the reservoir is an industrial thermal oil.

The invention also relates to the application of the closed-loop circulation installation to the closed-circuit preheating of a reservoir chronologically upstream of the hydrocarbon extraction phase.

One advantage of the invention lies in the production of a closed circuit enabling heat to be supplied to the well bottom. Thus, the heat is supplied both to the paraffin, asphaltene or lumps of bitumen which it melts, and to the liquid at the well bottom which it heats.

A further advantage of the invention lies in the fact that there is no mixture of the hot fluid and the recovered hydrocarbons thereby enabling the elimination of a hydrocarbon separation unit.

Another advantage of the invention lies in the absence of any pollution of the reservoir since the hot fluid does not contaminate this reservoir.

Yet another advantage of the invention lies in the use of fluid even polluting.

The hot fluid may be chosen from among the fluids used in heating installations, for example an industrial thermal oil or water.

The hot fluid leaving the heater circulates in the first thermally insulated tubing to its end and then returns to the surface between the first thermally insulated tubing and the second heating tubing. As it rises, the heat energy contained in the hot fluid is dissipated by conducto-convection in the oil produced in the drain and in the reservoir itself.

The temperature of the hot fluid is at its maximal at the surface as it leaves the heater. The thermal losses and thus the reduction in temperature of the fluid are low during its flow down in the thermally insulated tubing. When the hot fluid rises back up to the surface, the thermal exchanges with the oil produced in the drain are substantial to enable the exchange of heat and the temperature of the fluid drops considerably.

One advantage of the invention lies in the possibility of using an industrial thermal oil by way of heat transfer fluid. The necessary volume of oil in the closed loop formed by the first and second tubing is of between 500 litres and 3,000 litres. Such a thermal oil, standard in industry, will have an optimized composition to be heated to the required temperature, typically 200° C. or up to 300° C. and will enable to use surface equipment, pump and heater, to be used that is standard in industry and therefore less complex.

Indeed, heating a hydrocarbon mixture at temperatures of around 200° C. risks the creation of solid deposits on the heating elements of the boiler that can cause a reduction in the heating power or even an increase in the temperature of the heating element in question and its subsequent deterioration. The heating process of a thermal oil will be simpler since its composition is uniform and it will be selected such that it does not create deposits at the intended temperature.

Another advantage of the invention lies in that the quantity of water contained in the hydrocarbon produced no longer has an influence on the design of the heater. If there is water present in the hydrocarbon to be heated, from 0 to more than 90%, the heater will have to supply more energy to raise the temperature of the mixture by the same value and if steam appears, the efficiency of the exchanger drops.

Another advantage of the invention lies in that once the well head has been modified, this installation is independent from the other standard well production equipment and may thus be installed and removed according to the needs of the well leaving in place this standard production equipment at the well bottom and also at the surface.

Another advantage of the invention lies in the fact that the tubing enabling the closed-loop circulation of the hot fluid may be made using wound tubing called “coiled tubing”. The double-walled thermally insulated tubing may be made from two coiled tubing and inserted into the second tubing of greater diameter, which may also be coiled tubing. This triple tubing may be wound around a coiled tubing wheel for transportation purposes and installed in the well in a single operation by a “coiled tubing” unit. Specific parts are installed at each end of the coiled tubing to isolate or join the annulus as required for closed-loop circulation.

Another configuration of this invention is the use of this closed circuit circulation for the preheating of a reservoir chronologically upstream of the hydrocarbon extraction phase. Such preheating is necessary for certain heavy oil recovery methods such as SAGD (Steam-Assisted Gravity Drainage). In this configuration, there is no third tubing to bring up the hydrocarbons; it is merely a preheating phase of the reservoir. One advantage of this configuration lies in that this preheating may be performed using mobile surface equipment using thermal oil at high temperature, 200° C. or more. This preheating configuration may advantageously replace preheating by injection of steam for reasons of cost and scheduling of such operations in an oil field.

Other characteristics, particulars and advantages of the invention will become more apparent from the detailed description given hereafter by way of illustration and with reference to the drawings, in which:

FIG. 1 shows the upper part of an installation according to the invention,

FIG. 2 is a section made at the hydrocarbon reservoir,

FIG. 3 is a section along AA in FIG. 1, and

FIG. 4 is a section along BB in FIG. 2.

An oil well is generally constituted by two essential parts, an outer pipe, called casing, whose purpose is to consolidate the outer wall of the well in the ground and an inner pipe, called tubing, enabling the oil to be brought up to the surface. A screen or drain fulfils two functions: it ensures the filtering of the extracted crude oil which rises to the surface and it prevents the wellbore from collapsing into the productive zone. Different manual and automatic valves ensure the sealing and safety of the well with regard to the exterior. For more details, reference may be made to patent FR-2881788 which illustrates the production conditions of a well by heat supply.

The invention will now be described in greater detail, noting that FIG. 1 illustrates the upper and outer part of the wellbore and FIG. 2 shows the part at depth where the hydrocarbons to be extracted are located. As indicated previously, the aim is to heat the productive zone of the reservoir of a well so as to extract the hydrocarbons still present in the reservoir.

FIG. 1 partially shows the upper part of the extraction piping heating installation 1 according to the invention in which the vertical wellbore 2 is consolidated by a cylindrical metallic casing 3. This well is in relation with a reservoir as will be explained hereafter. In the metallic casing 3, hydrocarbon extraction means 4 at the surface and inside said casing 3 and means 5 enabling a hot fluid to be circulated from the surface to the reservoir to be heated and then back to the surface are introduced.

The extractions means 4 are constituted by an extraction unit 6 and a tubing 7 linking this unit to the hydrocarbon reservoir.

Means 5 comprise first thermally insulated tubing 8 to enable a hot fluid to circulate in a closed circuit from the surface to the reservoir and then back to the surface. This tubing 8 is linked to a continuous heating and injection unit for the hot fluid with continuous control of the temperature and flow rate. This heating unit comprises a storage 23 or expansion tank, a pump 10 and a heater 24. It goes without saying that this tubing 8 links the unit 9 to the hydrocarbon reservoir which is to be heated. The expansion tank 23 allows the increase in volume of the hot oil in the closed circuit to be accommodated thereby avoiding any overpressure in the circuit.

This first tubing 8 is surrounded by second tubing 11 to return the hot fluid to unit 9. Tubing 8 and 11 constitute a closed circuit with the hot fluid production unit 9 to enable this hot fluid to circulate continuously.

FIG. 2 shows the installation according to the invention at the hydrocarbon reservoir 12 that incorporates a substantially vertical part 13 and a substantially horizontal part 14 of length 1. This Figure also shows the casing 3 whose end is provided with radial perforations 15 at its end in the reservoir 12. These perforations enable the liquid 16 to enter into the casing 3. This part 14 of the casing is commonly called the screen and tubing 7, 8 and 11 are found in it. Tubing 7 extends from the surface to the beginning of the screen 14, as can be seen in the Figure.

In this screen 14 of the casing 3, first tubing 8 is open at its distal end 17 and second tubing 11 is closed at its distal end 18 by a transversal wall.

The insulation 21 may be made of a powder material commonly used in this domain. To reinforce the thermal insulation, the free space or annulus delimited between the two pipes 19 and 20 is subjected to reduced pressure. This reduced pressure may be between 1 and 100 mbar.

An electrical heating wire may also be provided and applied to the inner pipe 19 so as to reinforce the thermal supply to tubing 8 as will be explained with reference to FIGS. 3 and 4.

The hot fluid circulating in a closed circuit in the reservoir 12 may have a thermal activity. In heating the reservoir, it may have a dissolving activity so as to limit, reduce or suppress deposits, such as paraffin, asphaltene or lumps of bitumen, which as they solidify become deposited around the perforations 15 of casing 3, ultimately blocking them. Given that this is a closed circulation circuit, the reservoir 12 suffers no contamination from the fluid used.

The fact of using a hot fluid confers a two-fold effect. The heat enables the fractions that have already solidified or formed deposits to be melted. The heat, dissipated by conducto-convection in casing 3 filled with fluid then by conduction in the reservoir, additionally acts by reducing the viscosity of the hydrocarbon 16. The latter becomes more fluid when it is heated. By conduction through the reservoir rock 12, the heat sent will fluidize the hydrocarbons to be extracted and, in that way, will reduce the loss of head. Thus, for the same pumping power, a greater quantity of liquid will be extracted (improvement of productivity) and it will be possible to pump trapped liquid further in the reservoir (improvement of recoverable reserves)

Since the depth of the well may reach several hundreds of metres (100 to 2,000 m), it is essential in order to provide heat at the reservoir 12 level, to have highly thermally insulated tubing 8.

Thermally insulated tubing 8 is intended. Tubing 8 is made using the technique known as “pipe in pipe”. Between the two pipes 19 and 20 there is insulation 21.

The inner pipe 19 ensures the transportation of hot fluid. This pipe is mechanically protected by the second pipe 20 which has a greater diameter than the first one and is concentric to the first pipe 19 and is thermally protected by the insulation 21.

There are several possibilities available for the insulation between the two pipes 19 and 20. It is advantageous to provide crush-resistant insulation 21, acting as a spacer, either by its compressive strength or by the even addition of spacers between the first and second tubing, to prevent the two pipes 19 and 20 from coming into contact with one another. A microporous material may be used by way of insulation between pipes 19 and 20.

This microporous material, of the type described in patent FR-2746891, is advantageously obtained by compressing a powder, for example fumed silica. Such a compressed microporous material advantageously has a density of between 180 and 400 kg/m³. The thermal insulating capacities of such a material are considerably improved when it is placed in the annulus at low pressure between the two pipes 19 and 20.

Insulation 21 may also be made by providing a multi-layer super-insulation constituted by reflective screens separated by layers of powder, such as described in patent FR-03.13197. The screens are constituted by a reflective sheet, for example aluminium, onto which the powder is deposited, coiled in a spiral around itself. The powder has a granulometry substantially equal to 40 μm, pores whose size is in the order of magnitude of the mean free path of the gas molecules in which this powder is placed and a density of between 50 and 150 kg/m³. The thermal insulating capacities of such a material are significantly improved when it is placed at low pressure, between 10⁻² and 1 mbar, in the annulus between pipes 19 and 20. This insulation, as it does not have sufficient compressive strength properties, requires the addition of spacers regularly positioned between pipes 19 and 20. The material used for these spacers must have good insulating properties. Such a material may advantageously be a microporous material such as that described above.

Tubing such as that described previously enables sufficient heat to be supplied to make the hydrocarbons sufficiently fluid using a boiler of 20 to 500 KW.

The installation 1 according to the invention enables the production of crude oil to be increased by 20 to 500%, and enables abandoned reserves to be exploited and any pollution of the reservoirs to be avoided.

By way of illustration, tubing 8 according to the invention may be constituted by an outer pipe 20 with an external diameter of 33 mm and a thickness of 2 mm and an inner pipe 19 with an external diameter of 13 mm and a thickness of 2 mm and is able to transport 20 kW at 200° C. for an overall distance of 1,000 metres. In this example, the tubing 11 may be a pipe with an external diameter of 60 mm and with a thickness of 5 mm and the cylindrical casing may have a diameter of 178 mm in its vertical part and 114 mm in the drain or screen section.

Again by way of illustration, tubing 8 constituted by an outer pipe 20 with a diameter of 60 mm and a thickness of 6 mm and an inner pipe 19 with an external diameter of 33 mm and a width of 4 mm will easily transport 200 kW at 200° C. for an overall distance of 2,000 metres. In this case, tubing 11 may be a pipe of 89 mm with a thickness of 6 mm and the cylindrical casing may be of 244 mm in diameter in its vertical part and 178 mm or 140 mm in its drain or screen section.

FIG. 3 shows a section view along AA in FIG. 1 featuring the casing 3. In this casing, there is tubing 7, 8 and 11. The first tubing 8 is constituted by a first inner pipe 19 surrounded by a second concentric outer pipe 20 and insulation 21 housed in the space between the two pipes.

This Figure also shows the heating wire 22 positioned along the external wall of the inner pipe 19 from the surface.

It goes without saying that the different elements illustrated on this FIG. 3 are not drawn to scale and are only shown by way of illustration.

FIG. 4, which is a section view along BB in FIG. 2, shows the casing 3 equipped with tubing 8 and 11. As previously, the first tubing 8 is constituted by a first inner pipe 19 surrounded by a second concentric outer pipe 20 and insulation 21 housed in the space between the two pipes. The third tubing 7 goes from the surface to the beginning of the screen 14 or drain and is thus not shown in this Figure.

This Figure also shows the heating wire 22 positioned against the external wall of the inner pipe 19.

It goes without saying that the different elements illustrated on this FIG. 4 are not at scale and are only shown by way of illustration. 

1. A heating installation for the productive zone of the reservoir of a well for the extraction of hydrocarbons through the well linking the surface to this reservoir, comprising a substantially cylindrical casing consolidating said well and a hydrocarbon extraction means housed inside said casing and means enabling a hot heat-transfer fluid to be circulated from the surface to the reservoir, wherein it comprises through the well a first thermally insulated tubing of injection of the hot fluid from the surface to the reservoir, a second tubing surrounding the first tubing to return the hot fluid to the surface and a third tubing of extraction of the hydrocarbons independent from the first and second tubing, said tubings extending from the surface to the reservoir.
 2. The heating installation according to claim 1, wherein the first and second tubing are linked to a hot fluid production unit comprising a storage or an expansion tank, a pump and a heater to ensure a continuous circulation of the hot fluid in said tubing.
 3. The heating installation according to claim 1, wherein the first tubing is open at its distal end and the second tubing is closed at its distal end.
 4. The heating installation according to claim 1, wherein the first tubing is thermally insulated by means of a compression-resistant insulation.
 5. The heating installation according to claim 1, wherein the third tubing is linked to an extraction unit to bring the hydrocarbons produced in the screen or drain back to the surface.
 6. The heating installation according to claim 5, wherein the third tubing is open at its distal end and is provided with a well-bottom pump.
 7. The heating installation according to claim 1, wherein the first tubing is constituted by a first inner pipe surrounded by a second concentric outer pipe and by an insulation housed in the space between the two pipes.
 8. The heating installation according to claim 7, wherein the thermal insulation is a microporous material and in that a reduced pressure is established in the space between the two pipes.
 9. The heating installation according to claim 8, wherein the reduced pressure between the two pipes of the first tubing is of between 1 and 100 mbar.
 10. The heating installation according to claim 7, wherein the first tubing is provided with an electrical heating wire arranged against the outer wall of the inner pipe.
 11. The heating installation according to claim 1, wherein the heat-transfer fluid used to heat the reservoir is an industrial thermal oil or water.
 12. The application of the heating installation according to claim 1, to the closed-circuit preheating of a reservoir upstream of the hydrocarbon extraction phase. 